This invention relates generally to optics and more particularly to a system for and a method of replicating the known operational coolant fluid flow local pressure in an optical surface (such as a mirror surface) of a heat exchanger portion of a fluid cooled cylindrical optic to compensate for (and thereby eliminate or significantly reduce) any residual finish figure machining error of the optical surface, which said machining error is normally caused by the coolant fluid flow differential pressure deflection of the optical surface.
The technique presently used in an attempt to minimize the abovementioned figuring error involves filling the optic with water, attaching valved plugs to the coolant ports, and subsequently introducing a predetermined static pressure for figuring, i.e., finish figure or contour machining. Generally, the pressure used is predicted coolant average pressure, i.e., ##EQU1##
Since pressure loss in the passages in the optical surface of the heat exchanger portion of the cylindrical optic is usually the largest contributor to the difference between inlet and outlet pressures, it is apparent that large differences can exist between the operating (i.e., operational) pressure and the figuring (i.e., finish figuring machining) pressure. Typically, this results in optical figure error exhibiting a tilt across the heat exchanger for radial and involute passages, and as a local ripple due to the heat exchanger passage geometry, as will be shown later. Additionally, a local bulge or depression is exhibited where manifolds are located within the optical envelope.
One obvious solution to the pressure distortion problem is to duplicate actual coolant flow conditions during figuring. However, a number of problems make this undesirable. Either a very large "blowdown" coolant supply system or a recirculating pumped system is required. The latter would require a temperature control system to maintain coolant temperature. Coolant flow can introduce vibratory pressure fluctuations which can jitter the mirror during figuring. This, in turn, would introduce additional optical figure errors.
Accordingly, what is needed in the art, and is not presently available, is the capability to eliminate (or, at least, to significantly reduce) any residual finish figure machining error of the optical surface of the heat exchanger portion of the cylindrical optic, wherein the aforesaid residual error is caused by coolant fluid flow differential pressure deflection of the optical surface.